Arc tube cathode construction



July 1, 1958 B. P. DE LANY EI'AL 2,841,731

ARC TUBE CATHODE CONSTRUCTION Filed Jan. 21, 1954 M if INVENTORS SON DE LANY COPELAND BEATRICE PEAR PAUL L AT TO R NEYS United States Patent Ofiiice 2,841,?31 Patented July 1, 1958 ARC TUBE CATHODE CONSTRUCTION Beatrice Pearson De Lany, Miami Beach, Fla., and Paul L. Copeland, Chicago, Ill.

Application January 21, 1954, Serial No. 405,414

3 Claims. (Cl. 313-173) This invention relates to a tube of the general are type in which there are present an anode and a cathode between which there is a discharge and between which an arc is formed.

One of the objects of the invention is to provide a construction which facilitates the formation of the arc and vices or other accessories which may be cumbersome, un-

certain of operation and relatively expensive.

Another object is to provide a device of the type indicated in which the arc, after formation, will be confined to' a relatively small area of the cathode and will thus be stable in quality and in location.

A still further object is to provide in connection with the device of the type indicated means for covering or restricting a substantial part of a cathode pool area to confine the arc during the period of formation and thereafter to a limited area. p

Other objects will appear from time to time throughout the specification and claims.

The invention is illustrated more or less diagrammatically in the accompanying drawing, wherein: I

1 is an envelope of insulating material. It may normally be of glass and when completed, it is air tight and is substantially free from air. An anode 2 is provided and connected to a lead-in wire.

A cathode pool 3 is provided and is formed of mercury or caesium or any suitable metal which is fluid at normal operating temperatures. A lead-in wire 4 is introduced through the envelope 1 and is sealed and is in contact with the cathode pool 3 into which it projects.

5 is a restriction formed preferably of the material of whichthe main envelope 1 is formed. It may be of other material but is normally formed of the same material of the envelope and is joined to it by one or more supporting parts 6. These may be glass members, integral with the parts 1 and 5 and serve merely to position and support the bell-like member 5. The cathode pool 3 and the lower open end of the bell 5 are positioned so that the lower end of the bell is in contact with or somewhat submerged in the pool 3. As shown, it is somewhat beneath the upper level of the pool. A semi-conductive area 7 constitutes in efiect a cathode extension and is positioned on the inner face of the bell 5, adjacent but preferably not at its lower end. It is above the level of the cathode pool 3 and is out of contact with it. This cathode extension 7 is connected electrically to the cathode pool 3 by a member 8. As indicated, this is a line-like film of titanium or similar metal, drawn or otherwise applied to the inner surface of the lower end of the bell 5. It ex- 2. tends, when the parts are assembled,, from the cathode pool 3 to the cathode extension film 7. It is a resistance line and will be so referred to.

Although the bell 5 is substantially closed, except at its bottom, it will be provided with at least one perforation or opening 9. This opening is exaggerated as to size in the showing of the figure. It may be relatively minute. The invention is not limited to any particular size for this member, but if desired, the hole 9 may be enlarged and for some purposes it has real advantage when enlarged. The transition in the formation of the are from the glow to the arc stage is possible effectively when the hole is relatively large. Enlarging the hole appears to make the glow to are transition possible over a wider range of vapor pressure than otherwise would be possible and this satisfactory condition of transition is probably due to the presence of the cathode extension 7 which is in the form of a metallic film or other conductive or semiconductive film on the inside of the hell 5.

It has been found by experimentation that a hole 9 larger than 2 mm. in diameter, for example, makes pos sible the glow to are transition within the bell 5 at vapor pressures of only a few hundredths of a mm. Hg.

The cathode pool extension formed by the film 7 is as shown and as has been stated separate from the mercury pool cathode 3, but it is connected to it by a titanium or other resistance line which will preferably have a resistance of several thousand ohms. Satisfactory operation has been produced when the resistance of the resistance line 8 is between 4,000 ohms and 20,000 ohms. Although this resistance line or strip may be produced in any convenient fashion it is, under present conditions, satisfactory to produce the strip or line by drawing it by means of a titanium nail on the glass or other material which forms the bell 5. It is drawn, of course, on the inner surface and leads, in the assembled article from the film 7 to the cathode pool. A film of titanium might also be used for the same purpose when located to connect the cathode extension 7 and the cathode pool 3.

As a matter of convenience in manufacture, it has been found that if it is difiicult to cause the titanium to run off on the glass or to become fixed to the glass, it is well to immerse the glass of the hell 5 in water and this will assist in securing a good line of titanium posiinvention is not to be limited to the use of titanium in any form or in any manner of application as the resistance line connecting the cathode extension 7 with the cathode pool 3.

The cathode extension 7 may be produced in a variety of ways and the invention is not limited to any particular way of producing it. It might be formed by drawing a number of lines or by otherwise forming a film of material capable of acting as a cathode extension. The film might be painted on the inner surface of the glass. Several preparations are currently available. Among them is a form of colloidal graphite sold at the present under the trade name Aquadag.

The film might be produced by evaporation, and many different metals are capable of satisfactory evaporation and disposition to take the place of the layer or film 7. Whatever the material of which the cathode extension film is made and however it is applied to the inner surface of the bell 5, it is important that the film be positioned in such a manner that when the area which constitutes the cathode extension is Well covered, the connecting film or line which extends into the tip of the constriction is thin enough to provide the desired resistance across the film. The line as shown at 8 in the figure is merely illustrative of the fact that a relatively small area constitutes the line. It is not drawn to scale or to indicate the size or proportion required or permitted.

While the most satisfactory operation of: the device requires the film as a cathode extension and requires the connection or resistance line 8, the tube, with the physical constriction shown, including of course the bell'S, having the hole or perforation 9, will operate, after a fashion, but less efiiciently, even without the film.

In operation, the lead-in wires are connected to a source of electricity and when the potential diiference is sufficient, a glow will be set up on the exposed surface of the cathode pool 3. After the glow has been set up, the arc will develop rapidly and will be formed and will remain concentrated on the cathode pool within the bell. The potential. diiierence required to set up the glow and thus to start the arc is of the order of 1,000 volts or slightly in excess of that value.

After the glow has been set up and the are established, the arc will continue to run in proper stabilized manner on a current of about 200 ma. An important advantage which follows from the use of the hole 9 is that the transition from glow to are usually occurs as soon as the glow is established. This will occur so quickly that the glow itself is usually not separately visible. The use of a ingle fairly large hole, such as that indicated at 9, has proven entirely effective in accomplishing the glow formation and the glow to are transition.

in use, the glow is generally set up outside of the bell. The over voltage which is applied across the tube produces an obnormal cathode fall in the area of the cathode pool outside of the bell. This results in a large potential difference between the outside and the inside of the bell. As this occurs the discharge spreads inside the bell through the hole 9, and the concentration of the discharge through the hole provides the necessary conditions for setting up the arc. Thus the cathode spot and the arc with it are set up and maintained inside the restricting hell 5. The resistance 3, or its equivalent, prevents the spot from running up the inside of the bell onto the cathode extension area 7, and thus the resistance 8 assists in stabilizing the cathode spot and in stabilizing the location and condition of the arc.

We claim:

1. in combination in an electrical discharge tube comprising an air tight envelope formed of insulating material; a pool of metal therein which is in liquid form at normal operating temperatures, said pool comprising a cathode member, an anode positioned within said envelope and spaced away from said cathode; and electrical connections to said anode and said cathode from points outside of said envelope; and restriction means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said means comprising a member formed of insulating material positioned within said envelope and provided with a closed top and an open bottom, said open bottom being in contact with said metal pool; a portion of the interior of said restriction being provided with a conductive surface, spaced away from said metal pool, and a resistance connecting member positioned Li l on the inner face of said restriction and in contact with said conductive surface and with said metal pool; said member shaped to define an opening in the wall of said member between its ends, said opening establishing communication between the interior of said member and the interior of said envelope and means for positioning said restriction within said envelope.

2. In combination in an electrical discharge tube comprising an air tight envelope formed of insulating material; a pool of metal therein which is in liquid form at normal operating temperatures, said pool comprising a cathode member, andan anode positioned within said envelope and spaced away from said cathode; and electrical connections to said anode and said cathode from points outside of said envelope; and restriction means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said means comprising a member formed of insulating material positioned within said envelope and provided with a closed top and an open bottom, said open bottom being in contact with said metal pool; a portion of the interior of said restriction being provided with a conductive surface, spaced away from said metal pool, and a resistance connecting member positioned on the inner face of said restriction and in contact with said conductive surface and with said metal pool, said conductive surface comprising a cathode extension; said member shaped to define an opening in the wallet said member between its ends and above said conductive surface, said opening establishing communication between the interior of said member and the interior of said envelope and means for positioning said restriction within said envelope.

3. In combination in an electrical discharge tube comprising an air tight envelope formed of insulating material and substantially free from air; a pool of metal which is liquid at operating temperatures positioned Within said envelope, said pool comprising a cathode and an anode positioned within said envelope and spaced away from said cathode; electrical connections from the exterior of said envelope to said anode and said cathode, and means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said means comprising a generally hollow member having a closed top and an open bottom, said bottom being in contact with the said cathode metal pool and an opening in said restriction between its ends, said member having on its inner surface a semi-conductive film positioned out of contact with said metal cathode pool, and a resistance connection member formed of titanium and joining said semi-conductive film to said metal pool and means for positioning said member within said envelope and generally out of contact with said envelope and out of contact with said anode.

References Cited in the file of this patent V UNITED STATES PATENTS 7 1,064,116 Weintraub lunelO, 1913 1,156,227 Hewitt Oct. 12, 1915 2,147,484 Dobke Feb. 14, 1939 2,154,264 Damitz Apr. 11, 1939 2,431,637 Gaudenzi Nov. 25,1947 2,507,434 De Lany et a1. May 9, 1950 2,507,435 De Lany et al. May 9, 1950 2,673,303 De Lany et al Mar. 23, 1954 FOREIGN PATENTS 909,933 France JanJlO, 1946 

